Implement keyboard shortcuts and enrich note/task viewer views

Keyboard shortcuts (App.vue):
- g+h/n/t/p/c: navigate to home/notes/tasks/projects/chat
- n / t: new note / new task (when not in an input field)
- Escape: go home (when not typing)
- Shortcuts panel updated to document all working shortcuts

NoteViewerView:
- Context breadcrumb: parent note link (↑), project badge, milestone badge
- Fetches project and parent note titles in parallel on load
- Back button label improved to "← Notes"

TaskViewerView:
- Context breadcrumb: parent task link (uses parent_title from API), project badge, milestone badge
- Sub-tasks section with inline progress bar and status dots (clickable to advance)
- Sub-tasks loaded from /api/notes?parent_id=X&type=task
- Note type extended with optional parent_title field

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/types/note.ts

@@ -7,6 +7,7 @@ export interface Note {
   body: string;
   tags: string[];
   parent_id: number | null;
+  parent_title?: string | null;
   project_id: number | null;
   milestone_id: number | null;
   status: TaskStatus | null;